Connected: An Internet Encyclopedia
RFC 1771 - 9.2.1 Internal Updates

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### 9.2.1 Internal Updates

The Internal update process is concerned with the distribution of routing information to BGP speakers located in the local speaker's autonomous system.

When a BGP speaker receives an UPDATE message from another BGP speaker located in its own autonomous system, the receiving BGP speaker shall not re-distribute the routing information contained in that UPDATE message to other BGP speakers located in its own autonomous system.

When a BGP speaker receives a new route from a BGP speaker in a neighboring autonomous system, it shall advertise that route to all other BGP speakers in its autonomous system by means of an UPDATE message if any of the following conditions occur:

1. the degree of preference assigned to the newly received route by the local BGP speaker is higher than the degree of preference that the local speaker has assigned to other routes that have been received from BGP speakers in neighboring autonomous systems, or

2. there are no other routes that have been received from BGP speakers in neighboring autonomous systems, or

3. the newly received route is selected as a result of breaking a tie between several routes which have the highest degree of preference, and the same destination (the tie-breaking procedure is specified in 9.2.1.1).

When a BGP speaker receives an UPDATE message with a non-empty WITHDRAWN ROUTES field, it shall remove from its Adj-RIB-In all routes whose destinations was carried in this field (as IP prefixes). The speaker shall take the following additional steps:

1. if the corresponding feasible route had not been previously advertised, then no further action is necessary

2. if the corresponding feasible route had been previously advertised, then:

   1. if a new route is selected for advertisement that has the same Network Layer Reachability Information as the unfeasible routes, then the local BGP speaker shall advertise the replacement route

   2. if a replacement route is not available for advertisement, then the BGP speaker shall include the destinations of the unfeasible route (in form of IP prefixes) in the WITHDRAWN ROUTES field of an UPDATE message, and shall send this message to each peer to whom it had previously advertised the corresponding feasible route.

All feasible routes which are advertised shall be placed in the appropriate Adj-RIBs-Out, and all unfeasible routes which are advertised shall be removed from the Adj-RIBs-Out.

9.2.1.1 Breaking Ties (Internal Updates)

Next: 9.2.1.1 Breaking Ties (Internal Updates)

Connected: An Internet Encyclopedia
RFC 1771 - 9.2.1 Internal Updates